The present invention relates to a telecommunication circuit having an input impedance and containing current sources.
The present invention also relates to a telephone circuit, telephone and telecommunication device comprising such a telecommunication circuit.
Such telecommunication circuits containing current sources are known in the art of telephone apparatus from U.S. Pat. No. 5,226,078 in which they are described as being a useful tool in controlling the line current in a wired connection between the telephone exchange and the subscriber. At the subscriber end, a communication device, such as a telephone or facsimile or the like, has to have line transmission circuitry which has to perform a number of functions. Examples of required functions, apart from the actual transmission and reception, are:
termination of the line with a correct definite impedance, PA1 deriving of power from the line for feeding internal and/or peripheral devices and PA1 modulating the line current with an AC-signal to be transmitted. Details of these requirements may vary from country to country. These requirements should be layed down so as to form standards. However, even the standards are changed frequently. One of the features varying per country is the value of the terminating line impedance. The above-mentioned US patent mentions off-chip components that are apparently necessary for performing the adjustments required by the varying standards.